A new immunological reaction called cutaneous basophil hypersensitivity has recently been distinguished from classical tuberculin type delayed hypersenstivity. Recent work in our laboratory has shown that this delayed-in-time reaction featuring large accumulations of basophils, is transferrable by either immune lymphocytes or immune serum. The basic hypothesis to be investigated in this research proposal is that the serum transfers of basophil sensitivity are caused by specific antibodies and that the cell transfers are mediated by cells potentially able to make antibodies. Under the scheme that distinguishes "thymus derived" lymphocytes (T cells) from "bone marrow derived" or "Bursal equivalent" lymphocyte (B cells) cutaneous basophil hypersensitivity would thus be considered a B cell mediated reaction, while classical delayed hypersensitivity is a T cell mediated reaction. This application submits a comprehensive program for the investigation of basophil hypersensitivity and the characterization of the serum factors and immune cell types mediating this reaction. Serum factors transferring basophil reactions will be purified and characterized and appropriate in vitro correlative assays will be developed to demonstrate the serum components mediating this reaction. Experiments will seek to identify whether the immune lymphocytes mediating basophil sensitivity are T cells or B cells. This will be accomplished by studying cutaneous basophil hypersensitivity in desensitized guinea pigs made anergic for T cellmediated reactions and by quantitative studies on the localization of lymphoid cells transferring this reaction. In additional experiments the role of complement in basophil reactions will be studied in guinea pigs with acquired or congenital defects in the complement system.